The present invention relates to a fuel injection pump for supplying fuel to an internal combustion engine through fuel injection nozzles and, more particularly, to a fuel injection pump which can reduce combustion noise in an idling range of the engine and secure required output in other engine operating ranges.
Conventional injection rate control devices provided in fuel injection pumps include a type which is so arranged as to leak a portion of fuel to achieve a low rate of injection during low-speed running of an internal combustion engine, as disclosed in Japanese Provisional Utility Model Publications (Kokai) Nos. 59-131570 and 59-194564. However, such conventional fuel injection pump requires the provision of a means for causing the portion of fuel to be leaked, making the structure complicated.
Japanese Provisional Utility Model Publication (Kokai) No. 58-113869 discloses a fuel injection pump for an internal combustion engine, provided with an injection rate control device which utilizes a control circuit and an actuator for controlling the axial position of a control sleeve with respect to a plunger, to alter the portion of a cam to be used, in accordance with operating conditions of the engine, to thereby enable a reduction in noise in an idling range of the engine and secureness of required output in other engine operating ranges. To this end, the fuel injection pump is required to have an electronic control circuit, thus being high in cost.